In semiconductor processing, a semi-conducting wafer must be processed in a multiplicity of fabrication steps, i.e., as many as several hundred steps, in order to complete the manufacturing of an IC device. These processing steps may include etching, cleaning, deposition and various other processing procedures. A variety of chemicals, including various liquids and gases may be used, in the processing steps either to etch a specific feature on the IC chip, to clean after certain processing steps, to deposit layers from reactant chemicals, or to carry out other necessary processing steps.
For instance, in photomasking and metal cleaning processes, a variety of speciality chemicals are used. An important requirement for such speciality chemicals, i.e., photoresists, developers, spin-on glass and polyimide is the transporting and storage of the materials. In the case of a photoresist material, the photosensitivity and the lifetime of such material depends on its storage temperature. It is important to maintain such materials within a specification of 5 to 20.degree. C. for a photoresist/developer and -20 to 10.degree. C. for spin-on glass/polyimide materials.
The transporting of these speciality chemicals, especially liquids, or the delivery from a storage reservoir (i.e., a holding tank) to a processing chamber where the liquid is used is another important aspect of the fabrication process. A process liquid, such as that of a photoresist or a developer, can normally be transported in a fluid passage such as a stainless steel tubing by an electrical pump means. One of such conventional liquid delivery system for a photoresist is shown in FIG. 1.
As shown in FIG. 1, a photoresist delivery system 10 is shown in an illustration for the present invention novel method and apparatus. The photoresist delivery system 10 generally consists of a liquid reservoir 12 (or a holding tank), a nitrogen gas inlet 14, and a photoresist solution outlet 16. The nitrogen gas used is normally a dry nitrogen gas to pressurize the liquid reservoir 12. The liquid flow 18 out of the reservoir 12 which is pumped by an electric pump 32 assisted by the nitrogen pressure in the reservoir 12 first enters into a buffer tank 22 through inlet 24. The buffer tank 22 is used to regulate flow from the reservoir 12 and is also capable of separating a small amount of air bubbles in the liquid. A small amount of air bubbles can be exhausted from outlet 26 while liquid is fed through outlet 28 generally located at the bottom of the buffer tank 22 into an air controlled solenoid valve 34. The small amount of air bubbles exits outlet 26 on the buffer tank 22 and enters into a drain tank (not shown) through passageway 36. The air controlled solenoid valve 34 controlled by an air supply 38 regulates the amount of liquid that can be pumped through passageway 42.
In the conventional liquid dispensing line shown in FIG. 1, a second liquid reservoir tank (not shown) can also be used as a back-up supply for feeding into the electric pump 32 connected in parallel with the first liquid reservoir 12. A liquid flow 44 fed from the second liquid reservoir tank (not shown) enters into a second air controlled solenoid valve 46 controlled by the same air source 38 through passageway 48 into the electric pump 32. It should be noted that the first liquid reservoir 12 and the second liquid reservoir operate in an alternating fashion such that the refill or maintenance of one liquid reservoir can be conducted at anytime without interrupting the normal operation of the liquid dispensing line. The dual reservoir system therefore eliminates potential down time of the dispensing line.
The electric pump 32, assisted by dry nitrogen gas 52 pumps liquid flow 54 into a filter device 56. The filter device may also serve as an air bubble filter such that liquid flow 58 containing a small amount of air bubbles may exit the filter at outlet 60 into a drain tank 62. The liquid flow 58 is controlled by another air solenoid valve 64. A flow of the photoresist solution 66, controlled by a flow regulator 68 and a series of air pressure controllers 72 can be fed to a nozzle for the final dispensing of the photoresist solution through passageway 74.
During normal operations, a small amount of air bubbles can be purged out by the buffer tank 22 and the filter 56. However, when a large volume of air bubbles is generated, for instance, during a maintenance procedure of filter replacement or a refill of the photoresist solution in the holding tank 12, the buffer tank 22 and the filter 56 can no longer effectively exhaust the air bubbles. As a result, a flow of the photoresist solution 74 which contains a volume of air bubbles is applied to the surface of a wafer.
When a wafer surface is coated with a photoresist solution, the volume of the photoresist material deposited and the resulting photoresist film formed must be quantitatively controlled to a high accuracy. Since the presence of air bubbles in the photoresist solution decreases the amount of the photoresist material, the available photoresist material that can be applied to the wafer surface is reduced accordingly by the amount of the bubbles. A non-uniform coating and subsequently a defective pattern can be produced on the wafer. The flow regulating valve 68, also called a suckback valve, is designed to shut off the liquid flow or to suckback the flow when bubbles are detected flowing through the passageway 66. However, the valve 68 is not always effective in stopping the air bubbles. Furthermore, valve 68 sometimes causes the photoresist solution to drop onto the wafer surface after a normal dispensing time has lapsed and thus again causing a poor coating of the photoresist material.
It is therefore an object of the present invention to provide a method for eliminating air bubbles from a liquid dispensing line that does not have the drawbacks and shortcomings of the conventional methods.
It is another object of the present invention to provide a method for eliminating air bubbles from a liquid dispensing line by utilizing an air bubble tank positioned and connected in the line for collecting air bubbles in the liquid flow.
It is a further object of the present invention to provide a method for eliminating air bubbles from a liquid dispensing line by utilizing an air bubble tank which is capable of separating air bubbles from a liquid such that the bubbles can be cumulated in an upper portion of the tank for exhausting to the outside of the dispensing system.
It is still another object of the present invention to provide an apparatus for eliminating air bubbles from a liquid dispensing line by utilizing an air bubble tank equipped with a single inlet and two liquid outlets.
It is yet another object of the present invention to provide an apparatus for eliminating air bubbles from a liquid dispensing line which only requires a slight modification of an existing processing equipment.